The present invention generally relates to circuits for receiving and processing optoelectronic information. More particularly, the invention relates to circuits for detecting and amplifying a signal received from a light detecting device.
As the rate of data transfer between microelectronic devices increases, use of typical electrical bus schemes to transmit information becomes increasingly problematic. In particular, as the amount of information transfer increases, an amount of input/output power required to transmit information between devices and consequently an amount of electronic noise associated with the transmission increase.
Another problem associated with transmission of electrical signals using traditional electrical bus systems is that signal degradation increases as the rate of the transmitted signal increases. For example, when signals are transmitted at a rate of about 5 GHz using FR-4 substrate material, the signal suffers about a 60 dB loss across 10 cm. This loss can cause rise time degradation and amplitude loss for the signals as the higher order harmonics are filtered out. Accordingly, improved apparatus and systems for transmitting information between a plurality of microelectronic devices is desired. For the above reasons, although the majority of signal processing is done in the electrical domain, it has become highly advantageous to utilize optical communications to interconnect microelectronic devices.
In order to obtain the benefits of optical communications, optical signals must be detected, converted to electrical signals and vice versa. For this purpose, various optoelectronic devices have been developed and are available in the market place as individual devices as well as arrays. However, specialized circuits are needed to advantageously utilize this technology. For example, photo detectors provide low level current output signals that must be amplified and converted to voltage signals. Accordingly, there is a need for improved amplifiers to accept such low level currents and provide amplified and converted voltage signals. Moreover, there is a need for such an improved amplifier to provide robust operation over a wide range of ambient temperature, power supply voltage, and process variations.
The present invention provides improved circuits and techniques for detecting, amplifying and processing high speed signals received from an optical sensor. More particularly, low level electrical signals are converted to amplified voltage signals.
In accordance with one aspect of the invention, an improved transimpedance amplifier (TIA) suitable for converting current into voltage is provided. The TIA""s principal function is to interface a photo detector to an electronic system for applications such as data communications or other optical signal processing.
In accordance with the disclosed embodiments, the TIA of this invention embodies four stages: a common-base input preamplifier stage, a common-emitter voltage amplifier stage, common-collector isolation amplifier stage, an output buffer stage and a biasing circuit connected the base of the grounded base transistor in the input preamplifier stage. The described embodiments can be implemented in bipolar junction transistor (BJT), heterojunction bipolar transistor (HBT), MOSFET, CMOS, or any other complementary transistor technology. The details of those processes are well known to those skilled in the semiconductor arts and are not described in detail herein.